Hot work tool and method for producing same

ABSTRACT

The invention relates to a hot work tool, in particular a piercing mandrel or a rolling bar for producing seamless pipes or a forging mandrel for hot forging tubular workpieces made of metal, said tool having a main tool body ( 2 ), wherein at least one working area of the main tool body ( 2 ) is provided with a coating ( 4 ). In order to achieve an improved strength of the coating ( 4 ) on the main tool body, according to the invention the main tool body ( 2 ) has a profiled surface ( 5 ) and the coating ( 4 ) is applied to the profiled surface ( 5 ). The invention further relates to a method for producing such a hot work tool.

The invention relates to a hot-machining tool, particularly a piercing mandrel or a rolling bar for making seamless pipes, or a forging mandrel for hot forging tubular workpieces of metal, which machine tool has a base body, the machine-tool base body having a coating at least in a machining region. Furthermore, the invention relates to a method of making such a hot-machining tool.

A mandrel of this type for piercing round rods is known from DE 10 2008 056 988. Here, the machining region of the piercing mandrel is provided with a coating that reduces heat dissipation into the mandrel body during piercing and that firmly adheres to the mandrel body. For the function of the machine tool, it is essential that this layer be solidly anchored.

Furthermore, it is generally known in hot-machining tools or similar components, in order to increase the service life, to roughen the machining region, for example, before coating—in most cases, a thermochemical coating method—in order to improve the adhesion of the coating to be subsequently applied.

However, it has been shown that the rough surface often does not guarantee sufficient adhesion, and in many cases is lost during the coating process or during use. If thermal or mechanical stresses then act in the contact region between the base body and the coating, the protective layer peels off.

The object of invention is therefore to create a hot-machining tool of the above-described type, as well as a method of making it that ensures an improved bond between the base body of the machine tool and the coating. Accordingly, the hot-machining tool should have a longer service life, and making seamless pipes in particular is supposed to be more economically efficient.

This object is attained by the invention in that the machine-tool base body has a surface profiling, and that the coating is applied to the surface profiling.

The surface profiling preferably forms at least one inset anchor formation extending axially of the machine tool, the surface profiling particularly being formed by a plurality of ridges and grooves on the surface of the machine-tool base body.

The machine-tool base body preferably consists of steel.

The coating can be a layer that protects against thermal and mechanical stresses. It can be applied by a thermochemical coating method.

The method of making such a hot-machining tool has the following steps, according to the invention:

a) providing a machine-tool base body with a surface profiling preferably by mechanical machining, particularly by lathing;

b) applying a coating to the machine-tool base body.

In making the surface profiling, a plurality of ridges and grooves are preferably formed on the surface of the machine-tool base body that was previously machined smooth. In this connection, the ridges are particularly configured as projections that are ridges, preferably rectangular in radial cross-section, extending over a predetermined length along a longitudinal axis of the machine tool, and are raised above the grooves by a predetermined height. The grooves are preferably filled up with the coating, at least to the height of the ridges, during application of the coating according to step b), wherein preferably, the depth of the coating actually exceeds the height of the ridges.

After step a) and during step b), a part of the machine-tool base body can be subjected to thermochemical conversion that in particular comprises making an iron oxide, particularly preferably of scale.

Application of the coating according to step b) can also take place, for example, by flame spraying or plasma spraying.

Accordingly, an improvement in the bond between machine-tool base body and coating is achieved in that the surface of the metallic support material is machined smooth and then configured with a defined structure consisting of ridges and gaps spaced apart by the ridges and preferably produced by mechanical machining, particularly by lathing.

Subsequently, a part of the support material can be converted to a protective layer, by a targeted thermochemical coating method of the surface of this support material.

In this connection, the width as well as the height of the ridges and the depth of the gaps change accordingly. An additional outer protective layer is applied to this primary protective layer by the thermochemical method, and this layer simultaneously fills or closes the gaps or grooves that remain between the ridges.

Adhesion of the layer structure that has been formed is clearly improved by the structuring of the transition between the support material (base body) and the applied layer, which has previously been optimized, adapted in advance, in accordance with the conditions of use of the machine tool, and complete peeling off of the layer is prevented.

Aside from the improved transition between the rolled material and the oxide layer, the gripping behavior between the rolled material and the machine tool is also improved.

The proposed method of procedure or the configuration as described is suitable, in general, for machine tools and components that are supposed to be protected by means of a coating, in order to be better able to withstand thermal and mechanical stress.

Embodiments of the invention are shown schematically in the drawing. Therein:

FIG. 1 is a side view of a hot-machining tool in the form of a piercing mandrel;

FIG. 2 is a view of the detail shown at “Z” in FIG. 1 of the machine-tool base body before being coated;

FIG. 3 shows the detail Z according to FIG. 1 of the machine-tool base body after being coated;

FIG. 4 shows the detail Z according to FIG. 1 of an alternative embodiment of the coated machine-tool base body;

FIG. 5 is a first microsection of the detail Z of the hot-machining tool according to FIG. 1;

FIG. 6 is a second microsection of the detail Z of the hot work according to FIGS. 1.

In FIG. 1, a hot-machining tool 1 in the form of a piercing mandrel for making seamless pipe is shown. The machine tool 1 has a base body 2 that has a machining region 3 that extends through a predetermined length along an axis a. In the machining region 3, the machine tool 1 is provided with a coating 4 that protects the machine tool 1 from thermal and mechanical stress.

The precise structure of the machine tool, as a detail in the region Z according to FIG. 1, i.e. as a detail of the machine-tool base body 2, is shown in FIGS. 2 and 3. As can be seen, the radially outer surface of the machine-tool base body 2 has a surface profiling 5 consisting of a plurality of radially projecting ridges 6 that are disposed between grooves 7 that they form. The ridges 6 have an axial dimension B parallel to the axis a, which preferably lies in the range of approximately 250 μm to 4000 μm. A radial height D of the ridges 6 as compared with the grooves 7 lies in a range of approximately 500 μm to 5000 μm. A spacing A between two ridges 6 preferably lies in a range of approximately 200 μm to 2000 μm.

In this connection, the profiling 5 is applied to the surface of the base body 2 after it is machined smooth, and subsequently the recesses 7, which are block-shaped or rectangular in radial section, are machined in, particularly lathed in.

After this prior machining, the surface of the machine-tool base body 2 is provided with a coating 4, as shown in FIG. 3. In this connection, the total layer thickness C of the coating 4 fills the grooves 7 and exceeds the radial height of the ridges 6.

Seen parallel to the axis a, the material of the coating 4 is inset as a result of the surface profiling 5, so that the coating 4 adheres very firmly to the base body 2 during use of the machine tool 1.

In FIG. 4, a preferred embodiment or solution can be seen. The prior machining of the machine-tool base body 2 is done as in the solution according to FIG. 2 and FIG. 3, i.e. first the surface profiling 5 was machine into the smoothly machined base body 2. The progression of the profiling corresponds to that according to FIG. 2.

Then, however, part of the material of the base body 2 is converted to a protective layer, before application of the coating 4, at first by a thermochemical treatment. The converted material 8 runs in a layer of uniform thickness over the profiling 5 and is indicated with broken-line hatching. In this connection, the width of the ridges or elevated regions 6 decreases accordingly, as does the depth of the gaps, which again are rectangular in cross-section, as shown in FIG. 4.

The coating 4 is applied to the material layer 8 converted in this manner, i.e. to the primary or inner protective layer produced by conversion of the support material, during conversion or subsequently, as a second, outer layer, as FIG. 4 shows for the finished machine tool. This again takes place by a thermochemical method or, for example, by flame spraying or plasma spraying.

According to the solution shown in FIG. 4, a structure is therefore created between the support material (base body) 2 and the layer 4, before or during application or production of the layer 4 on the support material 2, which structure manifests itself in the converted material 8.

Examples of actual coatings can be derived from the representations in FIGS. 5 and 6. The inner, more porous layer 8 produced by conversion on the elevated regions or ridges 6 and the filling of the gaps or grooves 7 and the second outer layer 4 applied to the converted layer. The inner layer of converted material consists, in the present example, of iron oxides, and grows from the surface of the base body or the profiling. The gaps between the elevated regions or ridges are filled by the outer coating 4.

In the embodiment according to FIG. 5 and FIG. 6 the support material (tool base body) was coated with iron oxides, or the material of the base body was converted to iron oxides. The support material in the present case is steel. The maximum thickness of the coating on the base body amounts to approximately 1000 μm in this example.

The structured transition between the support material and the coating can be structured in optimized manner, depending on use, so that complete peeling of the layer during use can be prevented. As a result, the lifetime of the machine tool 1, in particular, can be significantly increased.

The surfaces of the coated tools can be smoothed before or during use, by means of mechanical machining such as grinding and polishing (before use) or rolling (during use).

Smoothing of the surface reduces the friction between the machine tool and the work piece (rolled material).

REFERENCE SYMBOL LIST

1 hot-machining tool

2 machine-tool base body

3 machining region

4 coating

5 surface profiling

6 ridge

7 groove

8 converted material

a axis direction

B length

D height

A distance

C total layer thickness 

1. A hot-machining tool, particularly a piercing mandrel or a rolling bar for making seamless pipes or a forging mandrel for hot forging of tubular work pieces made of metal, the machine tool having a base body, the machine-tool base body being provided with a coating at least in a machining region, wherein the machine-tool base body has a surface profiling and the coating is applied to the surface profiling.
 2. The hot-machining tool according to claim 1, wherein the surface profiling forms an undercut in an axis direction of the machine tool, the surface profiling particularly is formed by a plurality of ridges and grooves on the surface of the machine-tool base body.
 3. The hot-machining tool according to claim 1, wherein the machine-tool base body consists of steel.
 4. The hot-machining tool according to claim 1, wherein the coating is a layer that protects against thermal and mechanical stresses.
 5. The hot-machining tool according to claim 1, wherein the coating is applied by means of a thermochemical coating method.
 6. A method of making a piercing mandrel or a rolling bar for making seamless pipes or a forging mandrel for hot forging of tubular work pieces made of metal, wherein the method has the following steps: a) providing a machine-tool base body with a surface profiling by mechanical machining; b) applying a coating to the machine-tool base body.
 7. The method according to claim 6, wherein, to make the surface profiling, a plurality of raised regions and grooves are formed on the surface of the machine-tool base body, the raised regions being configured as projecting ridges that extend over a predetermined length along a longitudinal axis of the machine tool and that are raised above the grooves by a predetermined height.
 8. The method according to claim 7, wherein the grooves are filled with the coating, at least to the height of the ridges, during application of the coating according to step b) of claim 6, a preferably the surface of the coating exceeds the height of the ridges.
 9. The method according to claim 6, wherein after step a) and before step b) according to claim 6, part of the machine-tool base body is subjected to thermochemical conversion that in particular comprises making an iron oxide, particularly preferably of scale.
 10. The method according to claim 6, wherein application of the coating according to step b) of claim 6 takes place by flame spraying, plasma spraying, or by a thermochemical method.
 11. A method of making a piercing mandrel, the method comprising the steps of: machining into an outer surface of the mandrel an array of outwardly projecting ridges separated by outwardly open grooves; and applying a coating to the outer surface over the ridges and grooves that generally fills the grooves.
 12. The mandrel-making method defined in claim 11, wherein the coating is applied in a thickness greater than a depth of the grooves so as to cover and embed the ridges.
 13. The mandrel-making method defined in claim 11, further comprising the step after machining the formations into the outer surface and before applying the coating of: thermochemically converting an outer surface of the mandrel at the grooves and ridges so as to increase adherence of the coating to the tool.
 14. The mandrel-making method defined in claim 13 wherein the mandrel is of steel and the thermochemical conversion is oxide formation.
 15. The piercing mandrel made by the method of claim
 11. 